How do I iterate safely under modification with std::map for large datasets?

When working with large datasets in C++, iterating safely over a `std::map` that is being modified can be challenging. To avoid issues such as invalid iterators and undefined behavior, it is essential to understand the appropriate methodologies for synchronization and iteration.

One of the safest ways to iterate while allowing modifications is to use a copy of the keys or the values of the `std::map`. This ensures that even if the original map is modified during iteration, you are working with a stable set of data.

        std::map myMap = {{1, "one"}, {2, "two"}, {3, "three"}};

        std::vector keys;
        for (const auto& pair : myMap) {
            keys.push_back(pair.first); // Store keys in a separate vector
        }

        for (int key : keys) {
            // You can modify the map here, like removing an element
            if (key == 2) {
                myMap.erase(key);
            }
            std::cout << myMap[key] << std::endl; // Safe to access
        }